Use device labels rather than IDs in widget API

device IDs are different for each origin, so won't match up when passed
in & out of widgets. Use the label instead.

For https://github.com/vector-im/element-web/issues/23331

src/media-utils.ts

@@ -0,0 +1,23 @@
+/*
+Copyright 2022 Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export async function findDeviceByName(
+  deviceName: string
+): Promise<string | undefined> {
+  const devices = await navigator.mediaDevices.enumerateDevices();
+  const deviceInfo = devices.find((d) => d.label === deviceName);
+  return deviceInfo?.deviceId;
+}